a. Field of the Invention
This invention relates to axle shafts. In particular, the invention relates to a variable-wall light-weight drive axle shaft with an integral flange member and a method for forming the drive axle shaft.
b. Background Art
Axle shafts are often subjected to significant loads. Vehicle drive axle shafts, for example, transmit significant torque to the vehicle wheels and are subject to rapid starts and stops in operation. Because of the significant loads that are often imposed on axle shafts, most axle shafts are formed of solid metal to provide sufficient rigidity and strength. Solid axle shafts, however, require a significant amount of material and are relatively heavy. In vehicles, this weight has a negative effect on fuel economy and imposes additional loads on other vehicle components.
Because of the disadvantages associated with solid drive axle shafts, hollow drive axle shafts have been developed as shown, for example, in U.S. Pat. No. 5,213,250, the entire disclosure of which is incorporated herein by reference. Existing methods for forming hollow axle shafts, however, make it difficult to both quickly manufacture multiple axle shafts while also varying the inner and/or outer diameters of the shafts to achieve the objectives of a particular application for the shafts. Moreover, existing hollow drive axle shafts include a tubular body and a separately forged wheel flange that is friction welded to the body by rotating one or both of the flange and body relative to one another. The process of joining the wheel flange to the body requires a relatively large amount of time and manufacturing equipment and produces a joint between the flange and body that remains subject to fatigue and potential separation under certain loads.
The inventor herein has recognized a need for a drive axle shaft and a method for forming the drive axle shaft that will minimize and/or eliminate one or more of the above-identified deficiencies.